Dietary Fiber Intake and Risk of Advanced and Aggressive Forms of Prostate Cancer: A Pooled Analysis of 15 Prospective Cohort Studies

Background Evidence of an association between dietary fiber intake and risk of advanced and aggressive forms of prostate cancer (PC) and PC mortality is limited. Objective To examine associations between intakes of dietary fiber overall and by food source and risk of advanced and aggressive forms of PC. Design Pooled analysis of the primary data in 15 cohorts in three continents. Baseline dietary fiber intake was assessed using a validated food frequency questionnaire or diet history in each study. Participants/setting 842,149 men were followed for up to 9-22 years between 1985-2009 across studies. Main outcome measures The primary outcome measures were advanced (stage T4, N1, or M1 or PC mortality), advanced restricted (excluded men with missing stage and those with localized PC who died of PC), high grade (Gleason score ≥8 or poorly differentiated/undifferentiated) PC, and PC mortality. Statistical analysis Study-specific multivariable hazard ratios (MVHR) were calculated using Cox proportional hazards regression and pooled using random effects models. Results Intake of dietary fiber overall, from fruits, and from vegetables was not associated with risk of advanced (n=4,863), advanced restricted (n=2,978), or high-grade PC (n=9,673) or PC mortality (n=3,097). Dietary fiber intake from grains was inversely associated with advanced PC (MVHR comparing the highest vs. lowest quintile=0.84, 95% confidence interval [CI] 0.76-0.93), advanced restricted PC (MVHR=0.85, 95%CI 0.74-0.97), and PC mortality (MVHR=0.78, 95%CI 0.68-0.89); statistically significant trends were noted for each of these associations (p≤0.03), while a null association was observed for high grade PC for the same comparison (MVHR=1.00, 95%CI 0.93-1.07). The comparable results were 1.06 (95%CI 1.01-1.10, p-value, test for trend=0.002) for localized (n=35,199) and 1.05 (95%CI 0.99-1.11, , p-value, test for trend=0.04) for low/intermediate grade (n=34,366) PC. Conclusions Weak nonsignificant associations were observed between total dietary fiber intake and risk of advanced forms of PC, high grade PC, and PC mortality. High dietary fiber intake from grains was associated with a modestly lower risk of advanced forms of PC and PC mortality.